Miles per gallon - PatriciaX
Im trying to work out the maths here and its not working!

So, Im putting about 60 quid in the tank a week. I fill it up with around £35 a time and can run for approx. 500 miles on that amount.

Adding on about 100 miles for weekend runabouts etc. means Im doing 870 miles a week.

I work out that Im getting 30 mpg ... in a diesel? Is this right?

Granted, I usually motor at around 85 for about 650 miles of that total.

but 30 mpg in a diesel? Shouldn't I be getting more?

Patricia
x
Miles per gallon - CM
in short - yes. If you (like me) drive a 6 cyl diesel then you might expect +/- 34 mpg. Otherwise you should really get high 30s and 40s.

However if you have a prob with your diesel then this might explain a lack of mpg. Is the engine delivering power properly? Mine is playing up a bit and I set cruise control on the m'way at 75 mph and I was getting just over 25mpg!! I have changed where i fill up and will see over Xmas if thigns improve.
Miles per gallon - TrevorP
870 miles for £60 or 500 miles for £35 both work out at about 49mpg.
Which is OK.

(£60 at 75p / litre = about 80 litres, = 17.6 gallons)
Miles per gallon - SteveH42
I hope I don't sound too patronising in giving a little maths lesson here... (I suppose it's useful FAQ for many people)

Working out fuel consumption:

Preferably, measure how much you put in in litres, but in cost, simply divide by the price of the petrol, so in this case £35/75p (as an assumption) gives 46.66 litres.

Next, convert to gallons. The simple conversion is to divide by 4.544, but to work through, we divide the litres by .568 to give pints (82) and divide by 8 to give gallons = 10.27
(568ml is a pint and there are 8 pints to the gallon. .568 x 8 = 4.544)

And of course 500 miles divided by 10.27 gallons is 48.7 mpg

I only wish I got this mpg from my Yaris belting along at 85! I see the wisdom of going for the 1.3 if you get out of town much.
Miles per gallon - Baskerville
It doesn't sound like there's much wrong with this diesel, or the way you drive it. You must be relieved to find the best part of 49mpg is the real figure. Not bad at all for a big car like the Mondeo, even in purple.

Chris
Miles per gallon - daryld
I have mentioned this on this website before..what I am stating here is 100% honest with no blagging:

My 2000X Seat Arosa 1.7 diesel (non turbo) ALWAYS returns 76 MPG. I keep a fuel log and drive about 450 miles a week @ 60 MPH. befoer you start slagging me off for driving 'so slow' I find that driving the same route at 80MPH only saves, on average, 6 minutes each way due to the traffic on the A1.

You can save a fortune in fuel and wear by gentle use of the gas pedal, not accelerating hard, and only braking to stop (as per 'flow driving' technigue used by Police advanced drivers).

While writing I remember driving along the A428 being 'chased' by a Vectra who had worked hard accelerating to overtake me and several cars behind. When I caught up with him 10 minutes later on the A1 bottleneck I found that he was driving a LPG dual fuel Vectra: why bother when he simply could not drive economically in the first place??!!
Miles per gallon - Oz
daryld, I agree wholeheartedly.

I too drive 'smart', which doesn't mean slow, just unlike the goons on the motorway who follow in the overtaking lane at one-car-length intervals, constantly switching between accelerator and brake, using their fuel energy to heat the environment. These guys will be the first to complain about fuel prices.
When motorway driving comprised around half of my daily mileage, my BMW 320d always returned 56-60 mpg and occasionally over 60. I always got 700+ miles from a 63 litre tank and on one occasion over 840 (no, never run dry once).

Probably could do the run from Land's End to John o'Groats.
I spend the money I save on car-oriented holidays.

In answer to Patricia X, an Excel spreadsheet makes keeping tabs of all this a doddle (dates, litres, gallons, miles, kilometres - whatever relationships you want to know, on a graph if wished, etc.).
Miles per gallon - Ian Cook
Patricia

A simple rule of thumb that I've used for years.

45 mpg is 10 miles per litre (1 gallon being approx 4.5 litres). So if you travel 500 miles and put in 50 litres it's 45mpg, give or take a sniff.

If you put in 55 litres (for 500 miles) then you've used 10% more, so it's going to be aroung 40mpg.

This will do till you can get home with the calculator.

Ian Cook
Miles per gallon - CM
Why if it is ILLEGAL to sell anything in Imperial measures (note the case of the fruit seller who got a hefty fine for selling in lbs) are the government allowed to quote in mpg? A lot of local garages went out of business when they were made to comply to the law and change their old pumps reading gallons into the digital litre reading ones.

(IIRC the mpg figure of a car is supplied by a QUANGO)
Miles per gallon - CM
Is the UK getting rid of miles? Haven't heard that it is so can you tell us when this is going to happen? I know that we were trying to get everything metric but had not heard about changing miles to KM.

How much is this all going to cost? Do we have to change our speedos over to KM and would the m'way limit be 110kmh (or 68.75mph)? etc etc etc
Miles per gallon - J Bonington Jagworth
"Is the UK getting rid of miles?"

I hadn't heard that, either, and it remains illegal to signpost distances in km or, indeed, metres (has to be miles or yards). Frankly, I'd be happy to return to gallons, feet and pounds, which IMHO are much more human scale and sensible units. Decimals only matter for things that are regularly manipulated, like money, but it confuses things like measurements, where it is all too easy to be out by an order of magnitude.

What's your preferred quantity of beer, HJ?
Miles per gallon - PatriciaX
Thanks Guys, and no Steve, not taken as patronising at all: I just couldn't get my head around the conversion - I could never do it - still don't know the conversions for temperatures. I know that 0 is freezing and 100 is b***** hot!

49 mpg sounds a bit better. 30 was worrying me.

I agree totally on the "driving at 60 doesn't get you home quicker" but on the 77 mile drive home after a long day at work, I always start off with good intentions but speeding it up somewhat just satisfies me more: I *feel* like Im getting home sooner!

A few times, I have stuck to the 60 mph and I have definitely noticed the needle slowing down. I could probably do the whole week on one tank if I did the there-and-back at 60 but I know I just couldn't stick to it and have HGVs overtaking me. Mind you, its a more comfortable drive at 60 and Im not constantly waiting for b***** Novas to get out of my way in the fast lane ;)

Ian, your conversion sounds like the simple solution: Im not wanting a precise number if its around 45-ish as that'll do me fine.

thanks again

Patricia
x
Miles per gallon - SteveH42
As with most problems of this type there are 'general' and 'specific' solutions. If you usually put £35 in then, assuming about 75p a litre, this is not much over 10 gallons. For a 'near enough' value, assume 10 gallons as this makes the calculation easy. The 1.3mpg difference between the 'quick and dirty' 50mpg you get this way, and the 48.7 I got by working it through is nothing.

I had a similar system for the Tipo - typically I filled up with 36 litres which is 8 gallons. It's simple to divide the mileage by 8 to get a rough figure. For any car you just need to get a rough idea as to what your typical fill-up equates to, to the nearest gallon and use that figure. As Ian points out, a difference of even as much as a gallon only makes a fairly minor difference to the consumption figure.
Miles per gallon - BrianW
"still don't know the conversions for temperatures"

Simple (and accurate) to get celcius to farenheit is to double the celcius figure, deduct ten percent and add 32.

So: 30 celcius:
30 x 2 = 60.
10% of 60 is 6.
60 minus 6 is 54.
54 plus 32 is 86.

QED
Miles per gallon - SteveH42
Am I right in assuming both celcius and farenheit are linear scales? I recall one frustrating evening when I was trying to find out what temperature -40F was in celcius. It seemed to me that you just needed to know the celcius equivalent of 72F to get the temperature. (Negative of course!) but I was told that it doesn't work that way, but they couldn't give an explanation as to why not...

To get back on topic, my mother asked a good question when she first rode in my new Yaris. How come they can provide speed and distance in both miles and kilometres, but only show (outside) temperature in celcius and not farenheit?

Actually, as another aside, how do driving schools that use Yarii manage? The passenger cannot see the display, so cannot tell accurately how fast the car is going. I'd guess it would be simple to mod the secondary display to show speed as well, but does anyone know how this problem is resolved?
Miles per gallon - wowbagger
Am I right in assuming both celcius and farenheit are linear
scales? I recall one frustrating evening when I was trying to
find out what temperature -40F was in celcius. It seemed to
me that you just needed to know the celcius equivalent of
72F to get the temperature. (Negative of course!) but I was
told that it doesn\'t work that way, but they couldn\'t give
an explanation as to why not...


Hey! I can answer this one. Yes, they are both linear scales. The temperature scales originally derived from the expansion of certain liquids with increasing, errm, temperature. It turns out that the scale is linear with respect to the mean kinetic energy of the molecules whose temperature is being measured. Note, however, that the zero energy does not correspond to 0 celsius or 0 fahrenheit. It corresponds to absolute zero, or 0 Kelvins (note: Kelvins, not degrees Kelvin). A one Kelvin *increase* in temperature is the same as a one degree increase in celsius, but 0 Kelvins = -273.15 celsius.

A mistake commonly made is to think that 10 celsius is twice as hot as 5 celsius (for example). This is not so. In Kelvins the temperatures are (approx) 283 and 278, so actually the first is 283/278 times as hot as the second.

Although both Celsius and Fahrenheit are linear, the slope *and* origin are different (remember linear equations? y=mx c), so knowing the Celsius equivalent of one Fahrenheit temperature is not enough. For the record, 0C = 32F, 100C = 212F, and -40C = -40F. F= C * 9/5 32 and C= (F-32)*9/5

Apologies for nil motoring content.
Miles per gallon - SteveH42
Thanks, so I was right then! (I was factoring for the offset by getting the equivalent of 72F - i.e. -40F + 32F to take it to 0C)
Miles per gallon - BrianW
And, of course, you can do it in reverse.

To go from farenheit to celcius you subtract 32 then multiply what you've got by five ninths.

So boiling point is 212 farenheit.
Subtract 32 and you get 180.
Multiply 180 by five ninths and you get 100 = celcius.
Miles per gallon - Rebecca {P}
In the words of Miss Murphy my physics teacher circa 1981...

"If centigrade confuses you, as very well it might,
Nine fifths of 'C' plus 32 will give you farenheit"
Miles per gallon - HF
Good grief! You've just reminded me why I hated physics so much at school!
HF
Miles per gallon - Ken A
Hi All

Less accurate but puts you in the right ball park and can be done in the head without recourse to complex formulae. Double centigrade figure and add 30. ie 20c x 2 = 60 + 10 = 70.

Regards
KenA
Miles per gallon - Oz
Just for the record, in case you're an accuracy freak:

1 kilometre = 0.621371192 miles
1 litre = 0.219969152 gallons (Imperial, not U.S.)
Conversely
1 mile = 1.609344 kilometres
1 gallon (Imperial, not U.S.) = 4.546091 litres
Miles per gallon - Software - Pugugly {P}
Anyone know of a simple Fuel Managment Software. I had an excellent bit of kit (GSP ?) which died on 1st Jan. 2000.
Miles per gallon - dave18
I get got wound up at lower motorway speeds when trying to save fuel. 80-90, middle/outer lane ,flowing with the traffic is was most comfortable for me! :)
Miles per gallon - slefLX
Although for a while i've wanted to know how to work out mpg my brain is now frazzled with all this maths

ga ga ga ga
Miles per gallon - J Bonington Jagworth
If it's any help, I reset my trip meter when the fuel warning light comes on and refuel with a known (usually £20-worth) amount ASAP. Note the mileage the when the light comes on again (and reset the trip) and that is how far you went on that amount of fuel. If the fuel costs 75p/litre, say, a gallon is 4.54 times as much, in this case £3.40. £20 divided by £3.40 is 5.88 gallons, so mpg is your mileage divided by 5.88 (miles per gallon = miles divided by gallons).
Miles per gallon - Keith S
The light is not as accurate as brimming the tank each time.

Depends what you want.

By the way, there are centimeters between millimeters and meters ;)

Centigrade is sooooo easy. 0° = freezing 100° = boiling.

10° = winter midday
18° = start summer
30° = two days during summer :)
Miles per gallon - HF
10C = winter midday? We're struggling to get above zero here at the moment! And this is the sunny south not the blustering north!
HF
Miles per gallon - Mark (RLBS)
8:41pm 29 deg C

:-)
Miles per gallon - HF
Thank you for that gem of information, Mark, makes me feel so much better and warmer and - well, now I feel that I'm just enclosed by a golden globe of sunshine and warmth. Keep giving us the weather updates as the snow falls across Britain - honestly it really does keep the spirits up to see someone having to withstand sun and high temperatures, when obviously if they had the choice they'd be here making snowmen ;)
HF
Miles per gallon - J Bonington Jagworth
10C=50F. Another advantage of Fahrenheit - you get much nicer sounding temperatures.. :-)
Miles per gallon - Oz
Mark,
In England we have to contend with sparrow and blue-tit droppings on our cars. Must be hell in Chile with all those condors.

 

Value my car